Develop Reference

Sending image from server to client via base64 encoding

I'm facing an issues sending an Image (np.ndarray) over my python server to my javascript client.
Starting with the python server, I process the img like this:
1) Load img as np.ndarray
2) enc_img = base64.b64encode(img.copy(order='C'))
3) utf8_img = enc_img.decode("utf-8")
4) json = {
...
"img": utf8_img,
...
}
5) req_return = json.dumps(json, ensure_ascii=False)
// The fct below I found on SO ..
For the client (javascript) I do the following:
function b64EncodeUnicode(str) {
return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
return String.fromCharCode(parseInt(p1, 16))
}))
}
img_64 = b64EncodeUnicode(jsonRes.fs_dict.face)
var src = "data:image/jpg;base64,";
src += img_64;
var newImage = document.createElement('img');
newImage.src = src;
newImage.width = newImage.height = "100";
document.querySelector('#face_img').innerHTML = newImage.outerHTML;
To sum it up, I want to send an image over the API and convert it into a valid base64 format to display via html. After experimenting a little I sometimes got "no valid base64 format" but with the provided code I'm not getting any error. The image doesn't show up though.
It is important to not save the file in my scenario.

So I figured the problem. I had troubles encoding the image (nparray) to a proper base64 encoding.
pil_img = Image.fromarray(nparray_img)
buff = BytesIO()
pil_img.save(buff, format="JPEG")
enc_img = base64.b64encode(buff.getvalue()).decode("utf-8")
this resolved the encoding issues for me.
I then return a dictionary containing the img like so:
res = {
"img": enc_img
}
return res
After converting it to JSON via
json.dumps(res), I send it via the API to my JavaScript Client.
When receiving the JSON, I first parse it to access the dictionary again like so:
jsonRes = JSON.parse(xhr.responseText);
img = jsonRes.img;
and finally output it via HTML by using jQuery:
var source = "data:image/jpg;base64,";
source += img;
$(document).ready(function() {
$('#face_img').attr('src',source).height(100).width(100).show();
});
The
('#face_img')
is an ID of my HTML, looking like the following:
<img id="face_img" src="" alt="img_face" />
Hope this helps someone.

Sending videos from the client to the server

I recently read about the File API which allows the client to use files from the file system in the website.
I did all the stuff of adding the file input tag and reading the file and everything.
I read the file as ArrayBuffer using a FileReader and used a Uint8Array view on it, then I send the view to the server.
I tried it with txt, pdf and images and it worked fine. But when to use it with video files the computer lagged that and I didn't even wait and closed the browser!
Here's the code
Why did the lag happen with video files and is there a way to avoid it?!

I gone through the code, you are appending the read data pushed into the array which may be the reason why it lags.
You need to upload the video in chunks. To make a chunk of file you choose, you can take a look here
HTML5 file reader api
function readBlob(opt_startByte, opt_stopByte) {
var files = document.getElementById('files').files;
if (!files.length) {
alert('Please select a file!');
return;
}
var file = files[0];
var start = parseInt(opt_startByte) || 0;
var stop = parseInt(opt_stopByte) || file.size - 1;
var reader = new FileReader();
// If we use onloadend, we need to check the readyState.
reader.onloadend = function(evt) {
if (evt.target.readyState == FileReader.DONE) { // DONE == 2
document.getElementById('byte_content').textContent = evt.target.result;
document.getElementById('byte_range').textContent =
['Read bytes: ', start + 1, ' - ', stop + 1,
' of ', file.size, ' byte file'].join('');
}
};
var blob = file.slice(start, stop + 1);
reader.readAsBinaryString(blob);
}
document.querySelector('.readBytesButtons')
.addEventListener('click', function(evt) {
if (evt.target.tagName.toLowerCase() == 'button') {
var startByte = evt.target.getAttribute('data-startbyte');
var endByte = evt.target.getAttribute('data-endbyte');
readBlob(startByte, endByte);
}
}, false);
You need to modify according to your requirements. Here when you get the chunk, make a request to upload it or play it.
Also you can play with you video file here
Upload your Video file here to test
Hope this solves your problem. To get this working you need to handle the chunks properly on the backend as well.

Convert base64 to png in meteor app

I have a meteor application and in this one I get a base64 image. I want to save the image on a Digital Ocean instance, so I would convert it in a png or an other image format and send it to the server to get an url of the image.
But I didn't find a meteor package that does this.
Do you know how I can do that ?

I was running into a similar issue.
run the following:
meteor npm install --save file-api
This will allow the following code on the server for example:
import FileAPI from 'file-api';
const { File } = FileAPI;
const getFile = function(name,image){
const i = image.indexOf('base64,');
const buffer = Buffer.from(image.slice(i + 7), 'base64');
const file = new File({buffer: buffer, name, type: 'image/jpeg'});
return file;
}
Simply call it with any name of file you prefer, and the base64 string as the image parameter.
I hope this helps. I have tested this and it works on the server. I have not tested it on the client but I don't see why it wouldn't work.

I solved my problem using fs.writeFile from File System.
This is my javascript code on client side, I got a base64 image (img) from a plugin and when I click on my save button, I do this :
$("#saveImage").click(function() {
var img = $image.cropper("getDataURL")
preview.setAttribute('src', img);
insertionImage(img);
});
var insertionImage = function(img){
//some things...
Meteor.call('saveTileImage', img);
//some things...
}
And on the server side, I have :
Meteor.methods({
saveTileImage: function(fileData) {
var fs = Npm.require('fs');
var path = process.env.PWD + '/var/uploads/';
base64Data = fileData.replace(/^data:image\/png;base64,/, "");
base64Data += base64Data.replace('+', ' ');
binaryData = new Buffer(base64Data, 'base64').toString('binary');
var imageName = "tileImg_" + currentTileId + ".png";
fs.writeFile(path + imageName, binaryData, "binary", Meteor.bindEnvironment(function (err) {
if (err) {
throw (new Meteor.Error(500, 'Failed to save file.', err));
} else {
insertionTileImage(imageName);
}
}));
}
});
var insertionTileImage = function(fileName){
tiles.update({_id: currentTileId},{$set:{image: "upload/" + fileName}});
}
So, the meteor methods saveTileImage transform the base64 image into a png file and insertionTileImage upload it to the server.

BlobUrl, would it be a better option for you?
Save the images to a server as you like in base64 or whatever, and then when you are viewing the image on a page, generate the blobUrl of it. The url being used only at that time, preventing others from using your url on various websites and not overloading your image server ...

save image from canvas without increasing its size

I have a website where people can upload images and crop them before they upload them to the server.
My problem is that each image size increases by hundred percent in the upload process. For example if I take an JPG image size 102kb 640x640, when it is loaded from the website, I use the chrome network tool after I crea the cache and see that its size is 800kb (after I saved it with size 600x600).
In order to save it to the DB I use HTML5 canvas and cropping using http://fengyuanchen.github.io/cropper/
In the server side I use Azure CloudBlockBlob.
Client:
VData = $("#uploadedImage").cropper('getCroppedCanvas', {
width: 600,
height: 600
}).toDataURL();
Server:
public PhotoInfo UploadPhoto(string image, string picCaption)
{
string base64 = image.Substring(image.IndexOf(',') + 1);
byte[] imageByte = Convert.FromBase64String(base64);
Stream stream = new MemoryStream(imageByte);
// Retrieve storage account from connection string.
CloudStorageAccount storageAccount = CloudStorageAccount.Parse(
ConfigurationManager.AppSettings.Get("StorageConnectionString"));
// Create the blob client.
CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();
// Retrieve reference to a previously created container.
CloudBlobContainer container = blobClient.GetContainerReference("photos");
if (container.CreateIfNotExists())
{
// configure container for public access
var permissions = container.GetPermissions();
permissions.PublicAccess = BlobContainerPublicAccessType.Container;
container.SetPermissions(permissions);
}
// Retrieve reference to a blob
string uniqueBlobName = string.Format("{0}{1}", Guid.NewGuid().ToString(), Path.GetExtension("blob")).ToLowerInvariant();
CloudBlockBlob blob = container.GetBlockBlobReference(uniqueBlobName);
//blob.Properties.ContentType = image.ContentType;
blob.Properties.ContentType = "image/jpg";
stream.Position = 0;
blob.UploadFromStream(stream);
var photo = new PhotoInfo()
{
ImagePath = blob.Uri.ToString(),
InvitationId = 0,
Name = picCaption != null ? picCaption : ""
};
PhotoInfo uploadedPhoto = _boxItemProvider.SetPhoto(photo);
return uploadedPhoto;
}
Any advice here?
Thanks.

Issue was solved!
instead of just using toDataURL() with no parameters I replaced it with toDataURL("image/jpeg", quality) and image size was almost same as the original when the quality was 1 and 50% less when quality was 0.75

Save to Local File from Blob

I have a difficult question to you, which i'm struggling on for some time now.
I'm looking for a solution, where i can save a file to the users computer, without the local storage, because local storage has 5MB limit. I want the "Save to file"-dialog, but the data i want to save is only available in javascript and i would like to prevent sending the data back to the server and then send it again.
The use-case is, that the service im working on is saving compressed and encrypted chunks of the users data, so the server has no knowledge whats in those chunks and by sending the data back to the server, this would cause 4 times traffic and the server is receiving the unencrypted data, which would render the whole encryption useless.
I found a javascript function to save the data to the users computer with the "Save to file"-dialog, but the work on this has been discontinued and isnt fully supported. It's this: http://www.w3.org/TR/file-writer-api/
So since i have no window.saveAs, what is the way to save data from a Blob-object without sending everything to the server?
Would be great if i could get a hint, what to search for.
I know that this works, because MEGA is doing it, but i want my own solution :)

Your best option is to use a blob url (which is a special url that points to an object in the browser's memory) :
var myBlob = ...;
var blobUrl = URL.createObjectURL(myBlob);
Now you have the choice to simply redirect to this url (window.location.replace(blobUrl)), or to create a link to it. The second solution allows you to specify a default file name :
var link = document.createElement("a"); // Or maybe get it from the current document
link.href = blobUrl;
link.download = "aDefaultFileName.txt";
link.innerHTML = "Click here to download the file";
document.body.appendChild(link); // Or append it whereever you want

FileSaver.js implements saveAs for certain browsers that don't have it
https://github.com/eligrey/FileSaver.js
Tested with FileSaver.js 1.3.8 tested on Chromium 75 and Firefox 68, neither of which have saveAs.
The working principle seems to be to just create an <a element and click it with JavaScript oh the horrors of the web.
Here is a demo that save a blob generated with canvas.toBlob to your download folder with the chosen name mypng.png:
var canvas = document.getElementById("my-canvas");
var ctx = canvas.getContext("2d");
var pixel_size = 1;
function draw() {
console.log("draw");
for (x = 0; x < canvas.width; x += pixel_size) {
for (y = 0; y < canvas.height; y += pixel_size) {
var b = 0.5;
ctx.fillStyle =
"rgba(" +
(x / canvas.width) * 255 + "," +
(y / canvas.height) * 255 + "," +
b * 255 +
",255)"
;
ctx.fillRect(x, y, pixel_size, pixel_size);
}
}
canvas.toBlob(function(blob) {
saveAs(blob, 'mypng.png');
});
}
window.requestAnimationFrame(draw);
<canvas id="my-canvas" width="512" height="512" style="border:1px solid black;"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/FileSaver.js/1.3.8/FileSaver.min.js"></script>
Here is an animated version that downloads multiple images: Convert HTML5 Canvas Sequence to a Video File
See also:
how to save canvas as png image?
JavaScript: Create and save file

HERE is the direct way.
canvas.toBlob(function(blob){
console.log(typeof(blob)) //let you have 'blob' here
var blobUrl = URL.createObjectURL(blob);
var link = document.createElement("a"); // Or maybe get it from the current document
link.href = blobUrl;
link.download = "image.jpg";
link.innerHTML = "Click here to download the file";
document.body.appendChild(link); // Or append it whereever you want
document.querySelector('a').click() //can add an id to be specific if multiple anchor tag, and use #id
}, 'image/jpeg', 1); // JPEG at 100% quality
spent a while to come upto this solution, comment if this helps.
Thanks to Sebastien C's answer.

this node dependence was more utils fs-web;
npm i fs-web
Usage
import * as fs from 'fs-web';
async processFetch(url, file_path = 'cache-web') {
const fileName = `${file_path}/${url.split('/').reverse()[0]}`;
let cache_blob: Blob;
await fs.readString(fileName).then((blob) => {
cache_blob = blob;
}).catch(() => { });
if (!!cache_blob) {
this.prepareBlob(cache_blob);
console.log('FROM CACHE');
} else {
await fetch(url, {
headers: {},
}).then((response: any) => {
return response.blob();
}).then((blob: Blob) => {
fs.writeFile(fileName, blob).then(() => {
return fs.readString(fileName);
});
this.prepareBlob(blob);
});
}
}

From a file picker or input type=file file chooser, save the filename to local storage:
HTML:
<audio id="player1">Your browser does not support the audio element</audio>
JavaScript:
function picksinglefile() {
var fop = new Windows.Storage.Pickers.FileOpenPicker();
fop.suggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.musicLibrary;
fop.fileTypeFilter.replaceAll([".mp3", ".wav"]);
fop.pickSingleFileAsync().then(function (file) {
if (file) {
// save the file name to local storage
localStorage.setItem("alarmname$", file.name.toString());
} else {
alert("Operation Cancelled");
}
});
}
Then later in your code, when you want to play the file you selected, use the following, which gets the file using only it's name from the music library. (In the UWP package manifest, set your 'Capabilites' to include 'Music Library'.)
var l = Windows.Storage.KnownFolders.musicLibrary;
var f = localStorage.getItem("alarmname$").toString(); // retrieve file by name
l.getFileAsync(f).then(function (file) {
// storagefile file is available, create URL from it
var s = window.URL.createObjectURL(file);
var x = document.getElementById("player1");
x.setAttribute("src", s);
x.play();
});